The late comedy offering of the evening at the BT Studio this week is The Actor's Nightmare from Mercury Theatre Productions. It illustrates the age-old ordeal that we are told is the experiential lot which every actor undergoes – being called on stage to replace an absent colleague (Eddie, in a car crash) in an unfamiliar play at an unknown venue - and in your boxer shorts. And if you're an accountant rather than a thespian, then that just makes the task a touch more piquant. So George (or is it Stanley?) has to stand and deliver his part ('But presumably you know your lines?', he's asked), first from Noel Coward (Private Lives, was it?), then from Hamlet, then from Samuel Beckett's Happy Days, with nods to Waiting for Godot . But the farce and the tribulation multiply as he's propelled pell-mell into a new void of bewilderment.

The manic situation is studded with little comic squibs and director Alex Blanc, assisted by Anna Myrmus, cleverly keeps the pace high while instilling the necessary seriousness of treatment. Ryan Bernsten in the Victoria plum rôle of George, invented dialogue alternating with hapless soliloquizing directly in the tradition of Molière's Harpagon in L'Avare and Beaumarchais's Figaro in Le Mariage de Figaro, bursts with frustration as he vainly attempts communication with the stage manager and his interlocutors. From time to time he's by befuddlement reduced to uttering an irrelevant catchphrase: 'I wonder whose yacht that is over there!'. This is a performance of much force and comic desperation. Were Ryan towards the end to find just a little variation on shouting to express his fizzing bewilderment, his playing would be memorable.

He's heroically backed up by the vampish Chantal Marauta (especially good) in gorgeous gold dress ('When I cough three times that's the cue for you to unzip my dress!'), a boyish Horatio (coping manfully as his Prince of Denmark meanders from Elsinore to The Merchant of Venice via Macbeth) from Stevie Polywnka, Emilia Cieslak's outraged wife in glittering gold-and-black and later as the resigned Winnie, and Robin Ferguson's cross-dressing stage manager.

All the pressure and depressive humour and non-sequiturs of modern life were here in this offering from Mercury, from whom the Oxford student drama scene needs to hear much more.